G. C. Davenport. — Primitive Streak. 



PLATE V. 



Fig. 20. The sixty-fourth section behind the dorsal notochordal opening of a. 

 See Diagram I., page 6. X 240. 



Fig. 21. The one hundred and twelfth section behind the dorsal notochorda! 

 opening of a. X 240. 



Fig. 22. The region marked sii/. pf. p. in Fig. 17, more highly magnified 

 X 420. 



Fig. 23. The region marked siil. pr. p. in Fig. 18, under higher magnificatioa 

 X 420. 



Fig. 24. Section cut in the direction of the line 24-24, Fig. 5. The ectoderm 

 of a is split at the axis of a. The asterisk marks the point of 

 separation between the entoderm of a, and that of /3. X 73- 



Fig. 25. Section along the line 25-25, Fig. 5. The ectoderm of a is split at 

 the axis of a- One half of the entoderm of a has disappeared to- 

 gether with the anterior floor of ^. X 73- 



Note. — By an oversight a and ^" have been interchanged in position 

 in this Figure. 



Fig. 26. Section, the position of which is shown by the line 26-26, Fig. 5. 

 The ectoderm of a is split at the axis of a. Part of the entoderm 

 of a, and the anterior part of the floor of the notochordal canal of ^, 

 have broken through into the yolk. X 73- 



u. 



V 



\ 



